1. Field of the Invention
The invention relates to a protection arrangement for an inverter having fuses connected in series with its d-c inputs.
2. Description of the Prior Art
For converter installations which comprise a rectifier, an intermediate circuit and an inverter, an arrangement for protection against overvoltages is already known from German Pat. No. 911,034. In particular, in the aforesaid protection arrangement if an overvoltage occurs in the intermediate circuit due to a defect in the rectifier, this overvoltage is rendered harmless by a spark gap, by firing additional valves in the rectifier or by firing the rectifier valves. Thus, the latter protection arrangement is suited only for protecting for overvoltages in the intermediate link of a cycloconverter.
In inverters, on the other hand, in the event of a break in or failure of the d-c input voltage, the ability to fire and extinguish the valve branches for commutation is reduced. Typically such a break in or failure of the d-c input voltage occurs when a fuse in one of the d-c inputs of the inverter blows. In particular, in such case, there can develop in the semiconductor elements of the inverter, via an unblown fuse, an excessively high voltage or current leading to the destruction of the semiconductor elements within a very short time. Mechanical protection devices, therefore, cannot be used to reliably protect the inverter.
It is an object of the present invention to provide a protection arrangement for an inverter which protects the valve branches of the latter in the event of a break in or failure of the d-c input voltage.